import pygame
import sys


pygame.init()

size = width, height = 800, 600
bg = (255, 255, 255)

clock = pygame.time.Clock()
screen = pygame.display.set_mode(size)
pygame.display.set_caption('裁剪')

turtle = pygame.image.load('乌龟.jpg')

# 0 -> 未选择，1 -> 选择中，2 -> 完成选择
select = 0
#初始化一个方框
select_rect = pygame.Rect(0, 0, 0, 0)
# 0 -> 未拖拽，1 -> 拖拽中，2 -> 完成拖拽
drag = 0

position = turtle.get_rect()

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()

        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
                # 第一次点击，选择范围
                if select == 0 and drag == 0:
                    pos_start=event.pos
                    select=1
                # 第二次点击，推拽图像
                elif select == 2 and drag == 0:
                    capture=screen.subsurface(select_rect).copy()
                    cap_rect=capture.get_rect()
                    drag = 1
                # 第三次点击，初始化
                elif select == 2 and drag == 2:
                    select = 0
                    drag = 0

        elif event.type == pygame.MOUSEBUTTONUP:
            if event.button == 1:
                # 第一次释放，结束选择
                if select == 1 and drag == 0:
                    select = 2
                # 第二次释放，结束拖拽
                if select == 2 and drag == 1:
                    drag = 2
                
    screen.fill(bg)
    screen.blit(turtle, position)
    
    # 实时绘制选择框
    if select:
        mouse_pos = pygame.mouse.get_pos()
        if select == 1:
            pos_end = mouse_pos
        select_rect.left,select_rect.top = pos_start
        select_rect.width,select_rect.height = pos_end[0]-pos_start[0],\
                                               pos_end[1]-pos_start[1]
        pygame.draw.rect(screen,(0,0,0),select_rect,1)

    # 拖拽裁剪的图像
    if drag:
        if drag==1:
            cap_rect.center = mouse_pos
        screen.blit(capture,cap_rect)
            

    pygame.display.flip()    
    clock.tick(30)
